This patch adds two new painters located at gems/include/polygon_gfx.
Both painters draw convex polygons with an arbirary number of points.
The shaded-polygon painter interpolates the color and alpha values
whereas the textured-polygon painter applies a texture to the polygon.
The painters are accompanied by simplistic 3D routines located at
gems/include/nano3d/ and a corresponding example (gems/run/nano3d.run).
The headers 'texture_rgb565.h' and 'texture_rgb888' contain
template specializations needed for using the 'Texture::rgba' function
for the respective pixel formats. The specializations were formerly
contained in application-local code.
